Today, the production of blow moulded containers in different shapes and sizes—for example plastic bottles, pots, or other items—using the so-called cold cycle involves injection, compression, or extrusion moulding preforms or parisons made of a suitable plastic—for example, PET—and, then, cooling and storing the workpiece before the blow moulding process.
To use the injection or other type of press in the most efficient way possible, the preform cooling stage in the mould is kept to a minimum by transferring the preforms, as soon as possible, to specific external cooling stations, where cooling is completed.
To accomplish this, state-of-the-art sequential cooling stations can be used. Here, the preforms are cooled by placing them into specific cooling bowl-type holders cooled by water (a sequential cooling station is described, for example, in Patent Application WO 01/54883 filed by the Applicant). Said holders are placed in groups—often forming a square or rectangular layout—on cooling plates that are used sequentially, i.e. groups of preforms are handled in sequence: a group of preforms coming out of a mould—normally, all the preforms made with a single press blow—is placed in the holders of a plate to cool them simultaneously; then, the plate is freed of the cooled preforms and the station repeats the operating cycle.
Today, no continuous cooling stations—i.e. able to handle a continuous flow of preforms coming from a continuous moulding station, such as a rotary moulding station, described, for example, in patents EP 759 844 or U.S. Pat. No. 5,071,339—are known. It is currently not convenient to pair a sequential cooling station with a continuous moulding unit, especially a high production one.
Regardless of the moulding station, it is always desirable to make a cooling station that is sufficiently compact and small to occupy as little of the plant surface as possible.
After cooling, as was already mentioned, the preforms or parisons must be heated again—normally, by placing them on a chain or belt conveyor and feeding them through suitable furnaces—to make them reach a temperature suitable for the blow moulding process; often, said heating furnaces are infrared furnaces.
The drawback of today's infrared furnaces is that they are very large—especially lengthwise—in the case of plants with high production rates, which have a particularly fast chain conveyor speed.